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Re: M16#8 [#permalink] New post 12 Nov 2010, 12:05
hi guys

My respect to that person who created this question.

Here is very nice questions, which shows how tricky may be GMAT questions. Professionals who create such questions are also phycometrists - (or smth like that). They are sycologists who know how the logical flow of an ordinary person works and what are the gaps.
Most of you have realised that in 1) In the first 2 hours the bus.... - they talk about a part of total time
in 2) The average speed of the bus for the first half of the distance was - they talk about a part of total distance.

you want to solve it rapidly you have heard about half of and your brain does not want to care about this anymore.

This question may pretend to become one of my favorite questions.

Follow me, if you find my explanations useful.

Audaces fortuna juvat!

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Re: M16#8 [#permalink] New post 02 Feb 2011, 12:01
It took the bus 4 hours to get from town A to town B. What was the average speed of the bus for the trip?

1. In the first 2 hours the bus covered 100 miles
2. The average speed of the bus for the first half of the distance was twice its speed for the second half

Statement 1: This tells me that during the first 2 hours, the speed of the bus is 50mph.

Statement 2: This is not sufficient because I do not know the average speed of the bus during the first half of the distance or the second half of the distance.

Statement 3: We should NOT assume that during the first 2 hours of the trip, the bus has covered the first half of the distance. We do not know the total distance of the trip. Both statements will not give us the answer.

My answer is E. Very tricky C-trap question.
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Re: M16#8 [#permalink] New post 14 Feb 2011, 21:11
E. No where in the question does it state the total distance. You can be fooled into thinking C by assuming that 100 miles is half the distance. However it never states this.
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Re: M16#8 [#permalink] New post 04 Feb 2012, 05:59
Expert's post
This question is also discussed here: if-it-took-a-bus-4-hours-to-get-from-town-a-to-town-b-what-102361.html

There is a following trick in the question:

If (2) were: The constant speed of the bus for the first half of the distance was twice its constant speed for the second half.

Then for (1)+(2) we would have: s_1*\frac{4}{3}+\frac{s_1}{2}*(2-\frac{4}{3})=100 --> we can find s_1 so we can find d (d=2*s_1*\frac{4}{3}).

BUT: as it is now, we don't know whether the average speed after first \frac{4}{3} hours till 2 hours from the start was \frac{s_1}{2} or less or more, we just know that the average speed from first \frac{4}{3} hours till 4 hours from the start was \frac{s_1}{2}.

Hence the answer is E.

Hope it's clear.


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Re: M16#8 [#permalink] New post 06 Feb 2012, 02:53
The answer is E.
For solving this question we ought to know the distance between the towns A & B. Since none of the statements provide that so the answer is E.
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Re: M16#8 [#permalink] New post 08 Feb 2013, 02:56
Lets assume total distance = 2d.

we need to calculate 2d/4 = average speed for entire trip.

statement 1: tells us that bus travel 50MPH for first 2 hrs... clearly not sufficient.

statement 2: let 2v be the speed for first half, then v be the speed for second half.
d/2v + d/v = 4
d/4 = 2vsqure/3v
d/4 = 2/3 v.
as we don't know v. statement 2 is not sufficient.

combining st1 and 2. we can not calculate v. as 50 MPH given for first 2 hr and not first half of the journey.

Answer is E.

-------Analyze why option A in SC wrong-------

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Re: M16#8 [#permalink] New post 22 Jan 2014, 13:03
OA should be E.
There is no way we can calculate the Average speed.
From 1) we cannot say that 100 miles is half a distance. It might possible that 100 miles is only the one third of the distance and bus covers rest 2/3 distance in another 2 hrs. Making total of 4 hrs of total journey.
From 2) only gives the ratio of speeds for the first half to the second half.

Even using both these we cannot find the average speed.
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Re: M16#8 [#permalink] New post 20 Apr 2014, 07:45
1) No relation is drawn between the trip A-B and 100 miles -> insufficient
2) We need a specific figure for the ans -> also insufficient
Combine 2 stats:
From 2), the time spent on the first half of the trip is 1/2 that spent on the 2nd half => time spent on 1st half = 4/3hrs
-> from 1): 2a*4/3+a*2/3=100 -> a=30 -> average speed on the trip = [60*4/3+30*8/3]/4=40

Choose C
Re: M16#8   [#permalink] 20 Apr 2014, 07:45
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